1. Field of the Invention
The present invention relates to an image encoding method of encoding image data to obtain a predetermined code quantity and, more particularly, to a method which is suitably applied to a solid-state electronic still camera, an image communication, and the like.
2. Related Background Art
Conventionally, as one of compression encoding methods, variable-length encoding which varies the quantity of encoded data depending on image data is known. For example, an ADCT (Adaptive Discrete Cosine Transform) method examined by the so-called JPEG (Joint Photographic Expert Group) is known.
This encoding method requires a technique for changing a quantization parameter to converge a code quantity to a predetermined value.
However, when a plurality of images are input, a correlation of these images is not utilized to set a quantization parameter. For this reason, when a continuous photographing mode is set in, e.g., a solid-state electronic still camera, an arithmetic operation for setting a quantization parameter for one frame requires much time, and a continuous photographing speed is limited.
A technique for dividing one frame of a dynamic image to be transmitted into a plurality of blocks, changing a sampling density in units of blocks in accordance with a correlation among frames, and transmitting the image is proposed in U.S. Pat. Nos. 4,947,448, 4,755,878, and 4,916,537.
However, with the above-mentioned technique, there is room for improvement about a compression ratio of an image.